Employee Benefit Plans - Additional Information (Detail) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($) Plan	Sep. 30, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of foreign defined benefit plans | Plan					1
Pre-tax gain from net pension obligations					$ 7
Additional charge on defined benefit plan actuarial gain (loss)					3
Defined contribution plans expenses				$ 19	20	$ 19
Pension Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution			$ 5
Postretirement Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement medical benefits			$ 4
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 99		99	157
Settlement loss		$ 3
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible List]		us-gaap:OtherNonoperatingIncomeExpenseMember
Pension benefit obligation decreased				47
U.S. Defined Benefit Plans [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 6
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible List]	us-gaap:OtherNonoperatingIncomeExpenseMember
U.S. Defined Benefit Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss				3
Pre-tax gain from net pension obligations		$ (6)		(6)	(13)
U.S. Defined Benefit Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations		4		4	6
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		215		$ 215	205
Pension benefit obligation decreased					139
Foreign Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				41.00%
Foreign Plans [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				49.00%
Foreign Plans [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				6.00%
Foreign Plans [Member] | Cash and Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				4.00%
Foreign Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss				$ 1	(7)
Pre-tax gain from net pension obligations		(40)		(40)	(36)
Foreign Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations		$ (4)		$ (4)	(6)
U.K. Plan [Member] | Other Nonoperating Income (Expense) [Member]
Defined Benefit Plan Disclosure [Line Items]
Charge on effect of accrued benefit					$ 2